AVT Working Group L. Barbato
Internet-Draft Xiph.Org
Expires: December 28, 2006 June 26, 2006
draft-barbato-avt-rtp-theora-01RTP Payload Format for Theora Encoded Video
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on December 28, 2006.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document describes a RTP payload format for transporting Theora
encoded video. It details the RTP encapsulation mechanism for raw
Theora data and configuration headers necessary to configure the
decoder.
Also included within the document are the necessary details for the
use of Theora with MIME and Session Description Protocol (SDP).
Editors Note
Barbato Expires December 28, 2006 [Page 1]

Internet-Draft draft-barbato-avt-rtp-theora-01 June 20061. Introduction
Theora is a general purpose, lossy video codec. It is based on the
VP3 video codec produced by On2 Technologies and has been donated to
the Xiph.org Foundation.
Theora I is a block-based lossy transform codec that utilizes an 8 x
8 Type-II Discrete Cosine Transform and block-based motion
compensation. This places it in the same class of codecs as MPEG-1,
MPEG-2, MPEG-4, and H.263. The details of how individual blocks are
organized and how DCT coefficients are stored in the bitstream differ
substantially from these codecs, however. Theora supports only intra
frames (I frames in MPEG) and inter frames (P frames in MPEG).
Theora provides none of its own framing, synchronization, or
protection against transmission errors. Instead, the codec expects
to receive a discrete sequence of data packets. Theora is a free-
form variable bit rate (VBR) codec, and these packets have no minimum
size, maximum size, or fixed/expected size. Theora packets are thus
intended to be used with a transport mechanism that provides free-
form framing, synchronization, positioning, and error correction in
accordance with these design assumptions, such as Ogg [1] or RTP/AVP
[3].
Theora I currently supports progressive video data of arbitrary
dimensions at a constant frame rate in one of several Y'CbCr color
spaces. Three different chroma subsampling formats are supported:
4:2:0, 4:2:2, and 4:4:4. The Theora I format does not support
interlaced material, variable frame rates, bit-depths larger than 8
bits per component, nor alternate color spaces such as RGB or
arbitrary multi-channel spaces. Black and white content can be
efficiently encoded, however, because the uniform chroma planes
compress well. Arbitrary frame size will be encoded rounding to the
upper multiple of 16 both dimension for performance reason. The
original width and height will be encoded in the header and the
decoder will use this information to clip the decoded frame to the
right dimensions.
Theora is similar to the Vorbis audio [10] in that it the decoder
reads the probability model for the entropy coder and all
quantization parameters from special "header" packets at the start of
the compressed data. It is therefore impossible to decode any video
data without having previously fetched the codec info and codec setup
headers, although Theora can initiate decode at an arbitrary intra-
frame packet so long as the codec has been initialized with the
associated headers.
Barbato Expires December 28, 2006 [Page 3]

Internet-Draft draft-barbato-avt-rtp-theora-01 June 2006
This field identifies the version of RTP. The version used by this
specification is two (2).
Padding (P): 1 bit
Padding MAY be used with this payload format according to section 5.1
of [3].
Extension (X): 1 bit
The Extension bit is used in accordance with [3].
CSRC count (CC): 4 bits
The CSRC count is used in accordance with [3].
Marker (M): 1 bit
The Marker bit is used in accordance with [3].
Payload Type (PT): 7 bits
An RTP profile for a class of applications is expected to assign a
payload type for this format, or a dynamically allocated payload type
SHOULD be chosen which designates the payload as Theora.
Sequence number: 16 bits
The sequence number increments by one for each RTP data packet sent,
and may be used by the receiver to detect packet loss and to restore
packet sequence. This field is detailed further in [3].
Timestamp: 32 bits
A timestamp representing the presentation time of the first sample of
the first Theora packet in the RTP packet. The clock frequency MUST
be set to 90kHz.
SSRC/CSRC identifiers:
These two fields, 32 bits each with one SSRC field and a maximum of
16 CSRC fields, are as defined in [3].
2.2. Payload Header
The 4 octets following the RTP Header section are the Payload Header.
This header is split into a number of bitfields detailing the format
of the following Payload Data packets.
Barbato Expires December 28, 2006 [Page 5]

Internet-Draft draft-barbato-avt-rtp-theora-01 June 2006
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Configuration Ident | F |TDT|# pkts.|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+
Figure 2: Payload Header
Configuration Ident: 24 bits
This 24 bit field is used to associate the Theora data to a decoding
Packed Configuration.
Fragment type (F): 2 bit
This field is set according to the following list
0 = Not Fragmented
1 = Start Fragment
2 = Continuation Fragment
3 = End Fragment
This field must be zero if the number of packets field is non-zero.
Theora Data Type (TDT): 2 bits
This field sets the packet payload type for the Theora data. There
are currently three Theora payload types.
0 = Raw Theora payload
1 = Theora Packed Configuration payload
2 = Legacy Theora Comment payload
3 = Reserved
The packets with a TDT of value 3 MUST be ignored
The last 4 bits represent the number of complete packets in this
payload. This provides for a maximum number of 15 Theora packets in
the payload. If the packet contains fragmented data the number of
packets MUST be set to 0.
2.3. Payload Data
Each Theora payload section starts with a two octets length header
that is used to represent the size of the following data payload,
followed by the raw Theora packet data.
Barbato Expires December 28, 2006 [Page 6]

Internet-Draft draft-barbato-avt-rtp-theora-01 June 2006
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Configuration Ident | 0 | 0 | 2 pks |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Length | ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.. Theora data ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.. data | Payload Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.. Theora data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Example Theora Payload Packet
The payload portion of the packet begins with the 24 bit
Configuration ident field followed by 8 bits describing the payload.
The Fragment type field is set to 0, indicating that this packet
contains whole Theora frame data. The Data type field is set to 0
since it is theora raw data. The number of whole Theora data packets
is set to 2.
Each of the payload blocks starts with the two octets length field
followed by the variable length Theora packet data.
3. Configuration Headers
To decode a Theora stream three configuration header packets are
needed. The first, called the Identification Header, indicates the
frame dimensions, quality, blocks used and the version of the Theora
encoder used. The second, called the Comment Header, contains stream
metadata and the third, called the Setup Header, contains details of
the dequantization and Huffman tables.
Since this information must be transmitted reliably, and as the RTP
stream may change certain configuration data mid-session, there are
different methods for delivering this configuration data to a client,
both in-band and out-of-band which are detailed below. SDP delivery
is used to set up an initial state for the client application. The
changes may be due to different dequantization and Huffman tables as
well as different bitrates of the stream.
The delivery vectors in use are specified by an SDP attribute to
indicate the method and the optional URI where the Theora Packed
Configuration (Section 3.1.1) Packets could be fetched. Different
delivery methods MAY be advertised for the same session. The in-band
Barbato Expires December 28, 2006 [Page 8]

Internet-Draft draft-barbato-avt-rtp-theora-01 June 2006
codebook delivery SHOULD be considered as baseline, out-of-band
delivery methods that don't use RTP will not be described in this
document. For non chained streams, the Configuration delivery method
RECOMMENDED is inline the Packed Configuration (Section 3.1.1) in the
SDP as explained in the IANA considerations (Section 6.1)
The 24 bit Ident field is used to map which Configuration will be
used to decode a packet. When the Ident field changes, it indicates
that a change in the stream has taken place. The client application
MUST have in advance the correct configuration and if the client
detects a change in the Ident value and does not have this
information it MUST NOT decode the raw data associated until it
fetches the correct Configuration.
3.1. In-band Header Transmission
The Packed Configuration (Section 3.1.1) Payload is sent in-band with
the packet type bits set to match the payload type. Clients MUST be
capable of dealing with periodic re-transmission of the configuration
headers.
3.1.1. Packed Configuration
A Theora Packed Configuration is indicated with the payload type
field set to 1. Of the three headers, defined in the Theora I
specification [16], the identification and the setup will be packed
together, the comment header is completely suppressed. It is up to
the client to provide a minimal size comment header to the decoder if
required by the implementation.
Barbato Expires December 28, 2006 [Page 9]

Internet-Draft draft-barbato-avt-rtp-theora-01 June 2006
Intended usage: COMMON
Restriction on usage:
This media type does not depend on the transport.
Author:
Luca Barbato
Change controller:
IETF AVT Working Group
3.3. Loss of Configuration Headers
Unlike the loss of raw Theora payload data, the loss of a
configuration header can lead to a situation where it will not be
possible to successfully decode the stream.
A loss of a Configuration Packet results in the halting of stream
decoding and SHOULD be reported to the client as well as a loss
report sent via RTCP.
4. Comment Headers
When the payload type is set to 2, the packet contains the comment
metadata, such as artist name, track title and so on. These metadata
messages are not intended to be fully descriptive but to offer basic
title information. Clients MAY ignore them completely. The details
on the format of the comments can be found in the Theora
documentation [16].
Barbato Expires December 28, 2006 [Page 13]

Internet-Draft draft-barbato-avt-rtp-theora-01 June 2006
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC |M| PT | xxxx |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| xxxxx |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| synchronization source (SSRC) identifier |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| contributing source (CSRC) identifiers |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Configuration Ident | 0 | 2 | 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| length | Comment ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.. Comment ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.. Comment |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Comment Packet
The 2 byte length field is necessary since this Theora packet could
be fragmented.
5. Frame Packetizing
Each RTP packet contains either one complete Theora packet, one
Theora packet fragment, or an integer number of complete Theora
packets (up to a maximum of 15 packets, since the number of packets
is defined by a 4 bit value).
Any Theora data packet that is less than path MTU SHOULD be bundled
in the RTP packet with as many Theora packets as will fit, up to a
maximum of 15. Path MTU is detailed in [7] and [8].
A fragmented packet has a zero in the last four bits of the payload
header. The RTP packet containing the first fragment will set the
Fragment type to 1. Each RTP packet after the first will set the
Fragment type to 2 in the payload header. The RTP packet containing
the last fragment of the Theora packet will have the Fragment type
set to 3. If the fragmented Theora packet spans only two RTP
packets, the first will set the Fragment type field to 1 and the
second will set it to 2. To maintain the correct sequence for
fragmented packet reception the timestamp field of fragmented packets
Barbato Expires December 28, 2006 [Page 14]

Internet-Draft draft-barbato-avt-rtp-theora-01 June 2006
Packet 3:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC |M| PT | 1002 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| xxxxx |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| synchronization source (SSRC) identifier |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
| contributing source (CSRC) identifiers |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Configuration Ident | 3 | 0 | 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Length | ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
.. Theora data ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: Example Fragmented Packet (Packet 3)
This is the last Theora fragment packet. The Fragment type filed is
set to 3 and the packet count remains set to 0. As in the previous
packets the timestamp remains set to the first packet in the sequence
and the sequence number has been incremented.
5.2. Packet Loss
As there is no error correction within the Theora stream, packet loss
will result in a loss of signal. Packet loss is more of an issue for
fragmented Theora packets as the client will have to cope with the
handling of the Fragment type field. If we use the fragmented Theora
packet example above and the first packet is lost the client MUST
detect that the next packet has the packet count field set to 0 and
the Fragment type is set to 2 and MUST drop it. The next packet,
which is the final fragmented packet, MUST be dropped in the same
manner. Feedback reports on lost and dropped packets MUST be sent
back via RTCP.[note: reordering]
If a particular multicast session has a large number of participants
care must be taken to prevent an RTCP feedback implosion, [9], in the
event of packet loss from a large number of participants.
Loss of any of the Configuration fragment will result in the loss of
the full Configuration packet as detailed in the Loss of
Barbato Expires December 28, 2006 [Page 17]

Internet-Draft draft-barbato-avt-rtp-theora-01 June 2006
Configuration Headers (Section 3.3) section.
6. IANA Considerations
MIME media type name: video
MIME subtype: theora
Required Parameters:
sampling: Determines the chroma subsampling format.
width: Determines the number of pixels per line. This is an
integer between 1 and 1048561 and MUST be in multiples of 16.
height: Determines the number of lines per frame encoded. This is
an integer between 1 and 1048561 and MUST be in multiples of
16.
delivery-method: indicates the delivery methods in use, the
possible values are: inline, in_band, out_band/specific_name
Where "specific_name" is the name of the out of band delivery
method.
configuration: the base16 [11] (hexadecimal) representation of the
Packed Headers (Section 3.2.1).
Optional Parameters:
configuration-uri: the URI of the configuration headers in case of
out of band transmission. In the form of
"protocol://path/to/resource/". Depending on the specific
method the single ident packets could be retrived by their
number or aggregated in a single stream, aggregates MAY be
compressed using gzip [12] or bzip2 [14] and an sha1 [13]
checksum MAY be provided in the form of
"protocol://path/to/resource/aggregated.bz2!sha1hash"
Encoding considerations:
This media type is framed and contains binary data.
Security Considerations:
See Section 6 of RFC XXXX.
Barbato Expires December 28, 2006 [Page 18]

Internet-Draft draft-barbato-avt-rtp-theora-01 June 2006
Interoperability considerations:
None
Published specification:
RFC XXXX [RFC Editor: please replace by the RFC number of this
memo, when published]
Ogg Theora I specification: Codec setup and packet decode.
Available from the Xiph website, http://www.xiph.org
Applications which use this media type:
Audio streaming and conferencing tools
Additional information:
None
Person & email address to contact for further information:
Luca Barbato: <lu_zero@gentoo.org>
IETF Audio/Video Transport Working Group
Intended usage:
COMMON
Restriction on usage:
This media type depends on RTP framing, and hence is only defined
for transfer via RTP [3]
Author:
Luca Barbato
Change controller:
IETF AVT Working Group
6.1. Mapping MIME Parameters into SDP
The information carried in the MIME media type specification has a
specific mapping to fields in the Session Description Protocol (SDP)
[6], which is commonly used to describe RTP sessions. When SDP is
Barbato Expires December 28, 2006 [Page 19]

Internet-Draft draft-barbato-avt-rtp-theora-01 June 2006
used to specify sessions the mapping are as follows:
o The MIME type ("video") goes in SDP "m=" as the media name.
o The MIME subtype ("theora") goes in SDP "a=rtpmap" as the encoding
name.
o The clock rate in the "a=rtpmap" line MUST be 90000
o The mandated parameters "delivery-method" and "configuration" MUST
be included in the SDP "a=fmpt" attribute.
o The optional parameter "configuration-uri", when present, MUST be
included in the SDP "a=fmpt" attribute and MUST follow the
delivery-method that applies.
If the stream uses multiple decoder setup configurations and all of
them are known in advance, the Configuration Packet for each file
SHOULD be packaged together and passed to the client using the
configuration attribute.
The URI specified in the configuration-uri attribute MUST point to a
location where all of the Configuration Packets needed for the life
of the session reside.
6.1.1. SDP Example
The following example shows a basic SDP for a single stream. The
first configuration packet is inlined in the sdp, other
configurations could be fetched at any time from the first provided
uri using or all the known configuration could be downloaded using
the second uri. The inline base16 [11] configuration string is
omitted because of the lenght.
c=IN IP4 192.0.0.1
m=video RTP/AVP 98
a=rtpmap:98 theora/90000
a=fmtp:98 sampling=YCbCr-4:2:2; width=1280; height=720; delivery-
method=inline; configuration=base16string1; delivery-
method=out_band/rtsp; delivery-method=out_band/rtsp;
configuration-uri=rtsp://path/to/resource/; delivery-
method=out_band/http; configuration-uri=http://another/path/to/
resource/aggregate.bz2!sha1hash;
6.2. Usage with the SDP Offer/Answer Model
The offer, as described in An Offer/Answer Model Session Description
Protocol [5], may contain a large number of delivery methods per
single fmtp attribute, the answerer MUST remove every delivery-method
Barbato Expires December 28, 2006 [Page 20]

Internet-Draft draft-barbato-avt-rtp-theora-01 June 2006
and configuration-uri not supported. All the parameters MUST not be
altered on answer otherwise.
7. Examples
The following examples are common usage patterns that MAY be applied
in such situations, the main scope of this section is to explain
better usage of the transmission vectors.
7.1. Stream Video
This is one of the most common situation: one single server streaming
content in multicast, the clients may start a session at random time.
The content itself could be a mix of live stream, as the wj's voice
or studio scenes, and stored streams, as the music she plays.
In this situation we don't know in advance how many codebooks we will
use. The clients can join anytime and users expect to start the
fruition of the content in a short time.
On join the client will receive the current Configuration necessary
to decode the current streams inlined in the SDP so that the decoding
will start immediately after.
When the streamed content changes the new Configuration is sent in-
band before the actual stream, and the Configuration that has to be
sent inline in the SDP updated. Since the inline method is
unreliable, an out of band fallback is provided.
The client could choose to fetch the Configuration from the alternate
source as soon it discovers a Configuration packet got lost inline or
use selective retransmission [17], if the server supports the
feature.
A serverside optimization would be to keep an hash list of the
Configurations per session to avoid packing all of them and send the
same Configuration with different Ident tags
A clientside optimization would be to keep a tag list of the
Configurations per session and don't process configuration packets
already known.
8. Security Considerations
RTP packets using this payload format are subject to the security
considerations discussed in the RTP specification [3]. This implies
Barbato Expires December 28, 2006 [Page 21]

Internet-Draft draft-barbato-avt-rtp-theora-01 June 2006
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Barbato Expires December 28, 2006 [Page 25]